Post-deflection color tube



Nov. 26, 1963 P. RAIBOURN 3,112,359

POST-DEFLECTION COLOR TUBE Filed July 5, 1960 3 Sheets-Sheet 1 FIG. 2 FIG. 6 FIG. 7

INVENTQR PA L RAIBOURN BY TAM a ATTORNEY Nov. 26, 1963 Filed July 5. 1960 P. RAIBOURN POST-DEFLECTION COLOR TUBE 3 Sheets-Sheet 3 INVENTOR PAUL RAIBOURN ATTORNE Filed July 5, 1960, Ser. No. 40,744 10 Claims. (Cl. 1785.4)

This invention relates to the reception and display of color signals by means of a cathode ray tube and associated circuits, and more particularly to a cathode ray tube for display of television signals of the color subcarrier type, such as for example signals according to the NTSC standards. An example of the cathode ray tube of the invention is one of the post-deflection focusing type having a fluorescent screen on which are laid down strips of material which are fluorescent on electron impact in three primary colors. Color selection is achieved by means of a switching grid, the tube being generally of the type described in United States Patent No. 2,692,532. The invention provides a novel arrangement and disposition of the fluorescent strips on the screen in relation to each other and in relation to the conductors of the switching grid, with resulting improvement in color bal ance, brightness and resolution, and reduction in the power required at the switching grid for color selection. The mvention also provides more accurate and simplified means of decoding the subcarrier signal as compared with the prior art, as the prior art is set out for example in an article in the Proceedings of the Institute of Radio Engineers for January '1954- at pages 299 to 308.

The invention will now be described in detail in terms of a presently preferred embodiment with reference to the accompanying drawings in which FIG. 1 is a diagrammatic View of a cathode ray tube according to the invention;

FIG. 2 is a fragmentary view of the fluorescent screen of the tube of FIG. 1, showing at an enlarged scale the arrangement of color strips on the screen of a tube according to one embodiment of the invention and the relation thereof to the conductors of the switching grid in that tube;

FIG. 3 is a block diagram of a television receiver suitable for operation of the tube of FIGS. 1 and 2; FIG. 4 is a vector diagram useful in explaining the invention;

FIG. 5 is a set of waveforms useful in explaining the invention;

FIGS. 6 and 7 are two figures similar to FIG. 2 but illustrating other embodiments of the cathode ray tube of the inventionr The cathode ray tube of FIG. 1, generally indicated .at -1, comprises an electron gun generally indicated at 2,

disposed in the neck portion of an envelope 4. The gun develops a focused electron beam directed at a target area generally indicated at 6 and the beam is adapted to bescanned over the target area by means of scanning volt-ages of the usual type applied to crossed deflection coils 8 and 10. The scanning pattern may be that customarily employed for both black and white and color television signals, comprising two interlaced fields of mes.

The target area 6 includes a large number of side-byside strips 7 of material fluorescent on electron impact in three primary colors, typically red, blue and green, the

strips being laid down in a cyclically repeated order. For

brevity, the strips will hereinafter sometimes be referred to as red, green and blue strips to identify the color of the. light which they produce upon electron impact, in

view of the fact that these are the primary colors most often used. Others may be employed however and in FIG. 1 the three colors are identified as I, K, and L, and the cyclical order of strips is seen to be JKLK which is then repeated.

I United States Patent 0 For any set of three additive primaries, the invention comprehends the six different arrangements of the screen or target 6 in which those colors can be disposed in the cycle. For red, green and blue primaries, these arrangements are set forth in the accompanying table:

Table] RB GB RG GG RR BB BR BG GR GG RR BB The six arrangements are disposed in the table in three groups of two each, because of the similarity of the signals employed in the two embodiments of each group, as will be explained hereinafter.

For red, green and blue primaries, the presently preferred embodiment for television reception is number 1 in the table, in which the red strips are disposed electron-optically behind the grid conductors presently to be mentioned, with green strips, of which two strips are provided per cycle, one on each side of the red strip and adjacent thereto, and with a blue strip half way between adjacent red strips.

The tube includes between the gun and the target area, nearer the latter, a deflection grid generally indicated at 12. This grid includes two sets of mutually insulated conductors 14 and 16, which extend generally parallel to the strips and to the target area surface. Switching voltages may be applied between the two sets of grid conductors at electrodes 18 and 20, one of which connects with all conductors 14 and the other with all conductors 16. In FIG. 1 only a few of the grid conductors 14 and 16 are shown. In the tube as heretofore manufactured there may be of the order of 800 such conductors, 400' in each set. The spacing on centers of adjacent conductors may be of the order of 0.025 inch.

For simplicity of drawing, the tube face bearing the target 6 has been shown flat in FIG. 1. g It may be curved, and the switching grid may be adjusted in shape accordingly. Similarly, the thickness of the phosphor strips has been greatly exaggerated in order to illustrate their various colors. 7

The target area is overlaid on the side thereof adjacent the switching grid with a thin electron-permeable layer 22 by means of which, at a lead 11, a post-deflection focusing voltage may be applied between the target area and the mean potential of the switching grid.

Thus an accelerating voltage of the order of 5 kv. may be applied between the second anode 9 of the electron gun and the switching grid 12, for example to the. midpoint of a resistor connected between conductors 18 and 20, and a post-deflection voltage of the order of 15 kv. may be applied between the grid 12 and the conducting lay 22 on the screen 6.

This post-deflection voltage serves to constitute the grid wires together with the conducting layer 22 into a multiplicity of converging cylindrical electron lenses, one between each pair of adjacent grid wires and the screen, so that the electron beam undergoes a supplementary focusing in passing from the location of the grid to the screen.

The switching voltage applied to the grid conductors 14 and 16 serves to impose on the electron beam a supplementary deflection which directs the electron beam at appropriate times to strips on the target area of the proper color. The strips are of such width that in the dimension transverse to their lengh at least one strip of each primary color will be encountered in traversal of a distance less than the linear dimension of a picture ele- Patented Nov. 26., 1963 V ment. The strip width is accordingly of sub-elemental magnitude. The picture elements on the screen are selected in succession by the line and field scanning voltages applied to the deflection coils 8 and 10. Within each elemental area as so selected the sub-elemental area of appropriate color is selected by the switching voltage.

In cathode ray tubes for color television reception having a switching grid of the type hereinabove described, it has been customary heretofore to dispose behind (i.e. electron-optically behind) adjacent grid conductors strips of two colors alternately with a strip of the third color centered between the two conductors of each pair of adjacent conductors. In such a tube therefore there are as many strips of this last color as there are conductors in the switching grid and half as many strips of each of the other two colors.

Specifically, it has been customary to make the centered strip of green strip, with each red strip behind a conductor of one set and with each blue strip behind a conductor of the other set. Such a strip configuration is illustrated in FIG. 3 of Patent No. 2,745,035.

In a tube such as that of Patent No. 2,745,035 the electron beam will strike only the green strips when the two sets of grid conductors are at the same potential, the point of impact being shifted to red or blue strips by making the set of grid wires electron-optically in front of the strips of the desired color positive with respect to the other set of grid wires.

In accordance with the present invention, there are, as in Patent No. 2,745,035, twice as many strips of one color as of either of the other two colors, and the order of strips is JKLKJKLK. Instead however of positioning the strips with respect to the grid conductors such that adjacent strips of the colors I and L are disposed behind adjacent grid conductors, with the double color strips K centered between adjacent grid wires, the invention positions adjacent strips of only one of the single strip colors I and L behind adjacent grid conductors. This is illustrated in FIG. 1 from which it may also be seen that the color strip cycle JKLK has the same pitch as the pitch of adjacent grid conductors, instead of the pitch of two grid conductors as in the tube of Patent No. 2,745,035.

In FIG. 1 and in FIGS. 2, 6 and 7 the effects of parallax have been ignored; these figures may be considered on the assumption, made for convenience of representation in the drawings only, that the cathode ray beam reaches the switching grid oriented normally to the plane defined by the grid conductors.

With red, green and blue primaries in the system of color television signals to be displayed therefore, the invention comprises six embodiments with respect to the order of the phosphor strips, set forth in the Table 1 above. The embodiments numbered 1, 4 and 6 in that table are illustrated in FIGS. 2, 6 and 7 respectively.

Disposition and dimensioning of the strips on the screen with reference to the switching grid conductors and the spacing of the latter to compensate for curvature of the target area, if any, for parallax between the grid and screen and for variation in deflection sensitivity of the cathode ray beam over the target area may be made in accordance with the disclosures of Patents 2,745,033 and 2,745,035.

In FIG. 1, and hence in each of FIGS. 2, 6 and 7, there are four phosphor strips for each grid wire, and each such set of four strips contains one strip in each of two colors and two strips in the third color.

FIG. 2 shows a plan view of a portion of the target 6 of FIG. 1, adjacent switching grid conductors 14 and 16 being shown in front of adjacent red strips. The strip sequence is RGBG. The five strips on which the cathode ray beam may be focused within the color cell limited by adjacent conductors 14 and 16 are identified at 15, 17, 19, 21 and 23, and in the embodiment of FIG. 2 these are red, green, blue, green and red respectively.

The switching voltage employed on the grid 12 in the tube of FIG. 1 may advantageously be a sinusoidal one at color sub-carrier frequency. On FIG. 2 there has been drawn a circle 24 representing the locus of a vector rotating at uniform velocity. The displacements of the head of this vector from an axis 26 correspond to the displacements produced by the sinusoidal switching voltage applied to grid 12 of the cylindrical line focus of the cathode ray beam over that portion of the target between the conductors 14 and 16 between which the circle is shown.

In accordance with the invention the amplitude of the switching voltage is adjusted, with reference to the stiffness of the electron beam which depends upon the accelerating voltages applied to it, so that approximately one-eight of the duration of a switching cycle is expended by the cathode ray beam in each transition of a strip. By transition of a strip is here meant the passage of the focal spot of the beam onto a strip and off of it again, whether at the same side or the opposite side. -In the tube of the invention the beam spot has in the course of one cycle of the switching voltage two transitions of strips of the color 'I which are behind the grid wires (red, in FIG. 2,) two transitions over strips of the color L which are midway between the grid wires (blue, in FIG. 2), and four transitions over strips of the K color green, in FIG. 2), of which strips there are two in each cycle of color strips and hence two in each color cell defined by adjacent grid wires.

If the strips are all of the same width (which is not necessary), it is clear that the eight transitions cannot be of equal duration and hence cannot all equal oneeighth of a switching cycle. It is not necessary that the transitions be equal however in order to reproduce color pictures satisfactory to the viewer. Whatever the distribution of the switching cycle among transitions over stirps of the three colors, the phosphors of which the strips are made up are balanced as to their light output (in brightness units) for excitation by a cathode ray beam of constant intensity so that the tube will develop white light when the beam is unmodulated. One of the advantages of the tube of the invention is the fact that by adjustment of the amplitude of the switching voltage the transition times on the various colors may be adjusted with respect to each other. In this way compensation may be made for departures in tube manufacture from the desired balance among the phosphors.

FIG. 3 is a block diagram of a receiver suitable for operation of the tube of FIGS. 1 and 2. This receiver develops for application to a control electrode of the cathode ray tube, for example either its cathode 3 or its first control grid 5, a voltage which is the sum of an E E term at the second harmonic of the color subcarrier and an E -E term at the fourth harmonic of the color subcarrier. These signals occupy the band of chrominance frequencies, roughly from 2 to 4 mc. or from 3 to 4 mc. for NTSC signals. In addition the luminance signal over the zero to 4 me. range is applied to another control electrode of the cathode ray tube having opposite polarity effect, so as to efiect an additive combination of the signals applied to the two control electrodes.

In the block diagram of FIG. 3 there is shown at 30 a color television receiver which may be conventional and which performs all the customary functions of a television receiver up to that of the second detector. At the output of the receiver 30 there is shown a diode 31 which functions as a second detector. This second detector delivers to an amplifier 32 the complete video signal including luminance and chrominance, synchronizing signals for line and field scanning, and also the color synchronizing signal. In the NTSC signal this burst signal comprises a few cycles at color subcarrier frequency and fixed phase relative to the color subcarrier used in developing the chrominance at the transmitter, superimposed on the horizontal blanking pulses.

-vide switching voltage for the cathode ray tube.

From the detector 31 this total video signal is sent broadly through two channels. Amplifier 32 with a frequency selecting network 34 in its output serves to select the chrominance component in the 3-4 mc. range while the O to 3 mc. luminance component is developed across a frequency non-selective circuit illustratively shown as a resistor 36. The circuit for deriving from the video output of receiver 30 suitably timed line and field scanning voltages for application to the deflection coils 8 and 12 of tube 4 has been omitted from FIG. 3, since it may be entirely conventional. Similarly, the sound separating and amplifying circuits have been omitted, and there have also been omitted the circuits for developing accelerator voltages for the cathode ray tube, which may likewise be conventional.

The chrominance, after passage through a tfunther amplifier 38, is delivered through a further frequency selecting network 40 to an axis-selecting circuit shovm within a dash-line box 42. In addition it is delivered to a subcarrier regenerator 44 which has the function of generating under control of the burst a continuous oscillation at color subcarrier frequency and fixed phase with reference to that of the burst. The color subcarrier regenerator 44 also includes components from which the second, third and fifth harmonics of the color subcarrier are developed. A color subcarrier regenerator circuit is disclosed in the article entitled Compatible Color TV Receiver at pages '98 to 104 of Electronics for February 1953. The harmonic generators may comprise frequency multiplying circuits of conventional type and hence are not described in detail.

An additional function of the regenerator 44 is to pro- This voltage takes the form of a sinusoidal voltage of color subcarrier frequency, locked in phase with reference to the received burst signal, and applied in balanced fashion to conductors 18 and 20, advantageously through an adjustable phase-shifting network 45.

For the tube of FIG. 2, the desired monochrome component E may be of the form EM .25 E +.25 E +-5 E in view of the fact that, approximately, the dwell time of the cathode ray beam on green phosphor strips is twice as long as its dwell time on either of the blue and red phosphor strips.

With this make-up for the voltage E the E -E axis is approximately colinear with the E; axis in FIG. 4, neglecting the difference in amplitudes between the .63 E .59 E; and .45 E vectors of that figure and neglecting the departures of'their phases from a symmetrical 120", 120 positioning. On the same assump tions, the E E axis is orthogonal to the E E axis, and it is so shown in FIG. 4. I

The axis selection circuit 42 samples the chrominance output from circuit 40 along two axes at 90 to each other within the color subcarrier cycle. For the cathode ray tube of FIG. 2, these axes are the E E and E -E axes, which are shown in the vector diagram of FIG. 4.

The circuit 42 includes a multi-grid beam deflection tube 48 having a cathode 50, a first-control grid 52,. twin screen grid 54 and 56, two beam deflection electrodes 58 'and 60, and two anodes 62 and 64. The chrominance fromthe circuit 40 is applied to the first-control grid 52, and the beam deflection electrodes 58 and 60 are driven in push-pull from a transformer 66 which is fed at twice color subcarrier frequency from the regenerator 44. For brevity only, this second harmonic will be referred to as 7.2 me. which is approximately twice the frequency of the color subcarrier at 3.58 mc. in the NTSC signals. to operation with these frequencies, nor to operation The invention however is not restricted with the NTSC signals.

The phase of the signal applied to transformer 66 is 6 locked to the reconstituted subcarrier fundamental in regenerator 44 and can be adjusted with reference thereto by means of a phase control 68.

By means of the 7.2 mc. voltage applied to the deflection electrodes 58 and 60 in tube 48, current is caused to flow to the two anodes 62 and 64 at intervals of onequarter of the color subcarrier fundamental cycle.

The phasing of the signal applied to transformer 66 is adjusted so that conduction occurs at anode 62 at times centered about the E -E and (E E phases of the chrominance signal as applied to tube 48. Conduction accordingly occurs at anode 64 at times centered about the E E and (E E phases of that chrominance. These phases are indicated on the vector diagram of FIG. 4 wherein the vectors .63 E .45 E and .59 E identify, with respect to the burst, the phases of the color subcarrier cycle at which the chrominance is proportional to the red, blue and green primaries respectively.

On the same assumptions, the E E axis can be considered to be orthogonal to the E; axis and hence to the E E axis.

Returning then to FIG. 3, it is seen that a second harmonic signal applied in opposite phases to the two halves of the axis selection tube 48 will effect a sampling of the chrominance at 90 intervals of the color subcarrier cycle, i.e., along two orthogonal axes, and these may by proper phasing of the 7.2 mc. be made the E E and E E axes of FIG. 4. I

This is illustrated in FIG. 5 wherein waveform A rep resents the color subcarrier, i.e., a voltage of color subcarrier frequency having its maximum at the burst phase. Waveform B represents an arbitrarily assumed chrominance signal, such as might exist for example in the representation of a flat field of uniform color. The (ER, EB): (ER" EB) (EG EM) and ta- M) phases at which this chrominance is sampled are noted on waveform B, and waveforms C and D respectively represent the resulting A.C. voltages on anodes 62 and 64. While waveforms A through D have not only the same but also a common time scale so that the relative phases of those waveforms are indicated in the figure, no attempt has been made to show them in their'correct relative amplitudes.

The voltages C and D are seen to be of fixed phase with respect to the waveform A, irrespective of the phase or amplitude of the chrominance waveform B, but to be subject to changes in amplitude and polarity (i.e., 180 phase relation) with changes in the chrominance waveform B. The voltages of waveforms C and D, together with a suitable M (or Y) monochrome component, contain the information necessary to operate the tube of FIGS. 1 and 2. The E E and E E signals are however shifted in frequency to the second and fourth harmonics of the color subcarrier before application to the cathode ray tube. v

Specifically, a band-pass filter 69 delivers to a modulator 70 E -E voltage appearing on anode 62 in the 3 to 4 mc. range. This modulator also receives, from regenerator 44, the third harmonic of the color subcarrier through a phase control circuit 71. In the output of modulator 70 a frequency selective circuit 74 selects the difference between the inputs to the modulator, over a frequency range of from 6.7 to 7.7 mc., and this E E voltage at the second harmonic of color subcarrier frequency is passed through an amplifier 76 before being applied to an adding network 78.

In similar fashion a network 80 selects within the 3 to 4 mc. range the FI -E voltage on anode 64 of tube 48 and delivers it to a modulator 82, where it is mixed with the fifth harmonic of the color subcarrier supplied from regenerator 44 through a phase control '84. A circuit 86 in the output of modulator 82 selects the difference between the two modulator inputs over a frequency range of from about 13.8 to 14.8 mc. This E E voltage at the fourth harmonic of the color subcarrier is passed through an amplifier 88, having an adjustable gain, before application to the adder 78. This adder may be of conventional type, and the sum signal is applied to the first control grid of the cathode ray tube 4.

To the cathode of tube 4 then is applied the NTSC luminance signal E derived from detector 31, or alternatively a modified monochrome signal E =.25 E A-.25 E +.5 E A converter circuit for developing this E signal from E; is described at various places in the literature including US. Patent No. 2,814,778.

The propriety of these frequency shifted E -E and E -E voltages and the operation of the receiver of FIG. 3 therewith can be explained in a qualitative manner by consideration of FIG. 2 and of waveforms E, F, F, G and G of FIG. 5.

In FIG 5, waveforms E, F, F, G and G have a common time scale for the display of relative phases be tween them, but again no attempt has been made to illustrate the relative amplitudes of these waveforms, except that waveform G has been shown one-half the amplitudes of waveform G to indicate a 2 to 1 ratio of the amplitudes of those voltages, and waveforms F and F have been shown of the same amplitude to indicate that the voltages of which they are representative have the same amplitude. Waveforms E, F, F, G and G have the same time scale as waveforms A through D, but the two time scales, while of equal magnitude, are not common, so that there is no reference of phase relationship to be made between the two groups of waveforms.

From FIG. 2, it is apparent that red information is to be presented twice per switching cycle at 180 intervals thereof, and that the same is true of blue, adjacent red and blue areas being moreover spaced on centers by a quarter of the switching cycle. It is also apparent that green information is to be presented four times per switching cycle at 90 intervals thereof. The separation of adjacent blue and green areas is 45.

In FIG. 5 waveform E represents as a function of time the switching voltage applied to the grid 12 of the cathode ray tube, and there have been sketched in the red, green and blue phosphor areas to which this voltage carries the focal point of the cathode ray beams in its cyclical excursion. Waveform F shows, in full lines, the shape of the second harmonic output of modulator 70 assuming the scanning of a uniform red field at the transmitter. Waveform F shows in dotted lines the output of modulator 70 assuming the scanning of a uniform blue field at the transmitter. For a uniform green field, waveforms F and F fall to zero amplitude.

The full line waveform G of FIG. 5 shows the output of modulator 82 at the fourth harmonic of the color subcarrier assuming the transmitter to be scanning a uniform green field, and assuming the E E axis to be along the positive E axis in FIG. 4. Dashed line waveform G shows the fourth harmonic voltage E E assuming the transmitter to be scanning a uniform red or blue field. Waveform G is of half the R.M.S. amplitude of waveform G because, for E =l, E =0 and E =O, E =.5 and hence E E =.5 whereas for E =O and, say, either E =1 and E =0 or E =1 and E =0, E =.25 E =.2S or E =.25 and E =.25, so that E -E .25.

It is evident from inspection of waveforms F, F, G and G that with a flat green field the cathode ray tube will be caused by waveform G to conduct on the green portion of the switching cycle of waveform. E, and that with a bluefield the voltage of waveform F will combine with voltage G to cause the tube to conduct during the blue portions of the switching cycle.

Similarly, with a flat red field, Waveform F and wave- [form G will combine to cause conduction during the red portions of the switching cycle.

Looking now at FIG. 2, it may be seen that the fourth harmonic component E E if in the polarity of waveform G, as it will be for example in the case of a uniform green field, will tend to gate on the cathode ray beam, in a receiver employing the tube of FIG. 2, at each of the phases of the color switching cycle which carry the beam over the strips 17 and 2.1 of color K, which in the embodiment of FIG. 2 are green. For a uniform green field the second harmonic component E ;=E of Waveforms F and F is the zero amplitude and the tube produces green light only.

If, as for a field containing no green, the E --E component possesses the polarity of waveform G, that component will tend to gate on the cathode ray beam at the phases of the color switching cycle which bring the beam (or, more exactly, its point of focus on the target or screen) over the red and blue strips 15, 19 and 23. Under these circumstances the second harmonic waveform E E will, for a uniform red field, be of the polarity of waveform F (and it will of course be of non-zero amplitude) and it will tend to gate on the beam each time the beam passes over the red strip 15 and also when the beam passes over red. strip 23. The tendency of waveform G to gate on the tube over the blue strips is rendered harmless by the fact that E E voltage of waveform F is then at its negative maximum, thus preventing the development of unwanted blue light.

The foregoing qualitative explanation of the operation of the invention has been given with respect to solid color fields only. The operation of the invention is however of course not limited thereto.

FIGS. 6 and 7 illustrate, in a fashion similar to that of FIG. 2, two alternative embodiments of the invention in which the strip cycles are BRGR and GBRB respectively with the blue strips under the grid wires in FIG. 6 and the green strips under the wires in FIG. 7.

For operation of a tube according to FIG. 6, the receiver of FIG. 3 is modified, in the phasing of the 7.2 mc. voltage applied to transformer 66, so that circuit 42 sample the chrominance at E E and E E phases in FIG. 4. E -E is then converted in frequency to a second harmonic in modulator 70 and E -E is converted to a fourth harmonic in modulator 82.

Similarly, for operation of a tube according to FIG. 7, the receiver of FIG. 3 is modified in the phase of the voltage applied to transformer 66 so that circuit 42 samples the chrominance at the E E and E -E phase of FIG. 4.

The operation of tubes according to FIGS. 6 and 7 with the receiver of FIG. 3 modified as stated in the preceding two paragraphs may be explained qualitatively with the aid of the waveforms of FIG. 5, just as in the case of the tube of FIG. 2. To this end it is only necessary to identify waveforms F and F in FIG. 5 with the voltage EJEL delivered to amplifier 76 in FIG. 3, J identifying the color of the strips under the grid wires 14 and 16 and L identifying the color of the strips half way between the grid wires. Thus, generally stated, waveform F represents the voltage E --E delivered to amplifier 76 when the transmitter is scanning a uniform field in the color I which is the color of the strips under the grid wires, and waveform F represents the voltage E E when the transmitter is scanning a uniform field in the color L, which is the color of the other single strip located half way between the grid wires. Waveform G represents generally the voltage Ex-E delivered to amplifier 88 when the transmitter is scanning a flat field of the double strip color K, and Waveform G represents the voltage at the same point when the transmitter is scanning a field containing none of the color K.

Tubes with the strip configurations numbered 2, 3 and 5 in Table 1 above may be operated with receivers according to FIG. 3, and with the same signals selected in the output of modulators 70 and 82 as have been described for the tubes of FIGS. 2, 6 and 7 respectively, except that in each case the signal at the output of modulator 70 must be shifted 180" in phase in view of the interchange in colors between the J strips under the grid conductors and the L strips half way between grid conductors. Generally, the required signals may be described as E E at the second harmonic of the switching frequency and E E at the fourth harmonic of the switching frequency, with E =.25 EJ+.5 E +.25 EL' The tube of the invention is operable with other receivers than that shown in FIG. 3. Notably, the tube of the invention may be operated in a receiver in which the switching voltage applied to the grid 12 has a frequency one-half or one-quarter that of the color subcarrier. A receiver suitable for such operation of the tube of the invention may be derived from that of FIG. 3 by inserting a 2 for 1 frequency divider between the subcarrier regenerator 44 and the switching grid 12 of the cathode ray tube, by connecting anode 62 of tube 48 directly or through a suitable coupling network without frequency change to the adder 7'8, and by supplying modulator 82 with the third instead of the fifth harmonic of the subcarrier, modifying circuit 86 to select therein the second harmonic of the color subcarrier. The waveforms of FIG. may apply unchanged to such a receiver except that increments along the horizontal time scale in all of waveforms E, F,.F, G and G will represent only half the increments in time represented by the same distances in waveforms A through D. The ability of the tube of the invention to permit decoding while the tube is switched at half of color subcarrier frequency provides an important economy in switching power, and also makes it possible to dispense with the modulator 70 and a number of associated components.

Another advantage of the tube of the invention is the fact that the fundamental of the color subcarrier frequency, and the odd harmonics thereof, if they leak into the cathode ray tube as modulations on the cathode ray beam, serve only to desaturate the reproduced picture by adding white to it and do not inject false colors. This is of importance because of the necessary presence in the receiver of signals at odd multiples of the color subcarrier for the purpose of presenting axis-selected components at the desired second and fourth harmonics of the color subcarrier.

I claim:

1. A cathode ray tube comprising an electron gun, a target area having a multiplicity of strips of material disposed thereon in side-'by-side relation, said strips being luminescent on electron impact in a plurality of primary colors J, K and L additive to produce white, and a grid including two sets of insulated interlaced conductors arranged with said conductors substantially parallel to said strips between said gun and target area, adjacent of said conductors being electrically insulated from each other and alternate of said conductors being electrically con nected together, said strips being laid down in a repeating cyclical onder JKLK with adjacent strips of the color I disposed electron-optically behind adjacent of said conductors with respect to said gun.

2. A cathode ray tube according to claim 1 in which the color K is red.

3. A cathode ray tube according to claim 1 in which the color I is red.

4. A cathode ray tube according to claim 1 in which the color L is red.

5. A cathode ray tube comprising an electron gun, a target area having a multiplicity of strips of material disposed thereon in side-by-side relation, said strips being luminescent on electron impact in a plunality of primary colors red, blue and green, and a grid including two sets of insulated interlaced conductors arranged with said conductors substantially parallel to said strips between said gun and target area, adjacent of said conductors being electrically insulated from each other and alternate of said conductors being electrically connected together, said 10 strips being laid down in a repeating cyclical order red, green, blue, green with red strips disposed electronoptically behind adjacent of said conductors with respect to said gun.

6. A cathode ray tube for the display of color television images of the color subcarr'ier tylpe employing three primary colors J, K and L additive to produce white, said tube comprising an electron gun, a target area across which a beam of cathode rays from said gun is adapted to be bidimensionally scanned, a multiplicity of strips of material each luminiscent on electron impact in one of the colors I, K and L laid down side-by-side on said target, and a :grid of conductors disposed between said gun and target with said conductors generally parallel to the length of said strips, adjacent of said conductors being electrically insulated from each other and alternate of said conductors being electrically connected together, said conductors having a substantially uniform spacing of the order of magnitude of the maximum dimension of a picture element in the picture to be reproduced in said tube, said strips being laid down in a repeating cyclic order JKLK with adjacent strips of the color I disposed electronoptical-ly with respect to said gun behind adjacent conductors of said grid and with each strip of the color L electron-optically centered with respect to said gun between adjacent of said conductors.

7. A cathode ray tube comprising an electron gun, a target having thereon a multiplicity of substantially parallel phosphor strips luminescent on electron impact in three primary colors J, K and L additive to produce white light, and a multiplicity of linear conductors mounted between said target and electron gun, said conductors extending substantially parallel to said strips, alternate of said conductors being connected together and adjacent of said conductors being mutually insulated, said strips being laid down in a repeating cyclical order JKLK with adjacent strips of the color I electron-optically disposed behind adj-acent of said conductors, the strips of the color I being less elficient than strips of the colors K and L in producing light from the energy of cathode rays incident thereon.

8. A cathode ray tube comprising an electron gun, a target area having a multiplicity of strips of material dis posed thereon in side-by-side relation, said strips being luminescent on electron impact in a plurality of primary colors J, K and L additive to produce White, and a grid including two sets of insulated interlaced conductors arranged with said conductors substantially parallel to said strips between said gun and target area, said strips being laid down in a repeating cyclical order JKLK with adjacent strips of the color I disposed electron-optically behind adjacent of said conductors with respect to said gun, said strips fluorescent in the color I being less efiicient than strips of the colors K and L in producing light from the energy of cathode rays incident thereon and being wider than said conductors whereby a beam of cathode rays generated in said gun may impact said strips of the color I from either side of the conductors behind which they are centered.

9. A television receiver for the display of color television signals of the color subcarrier type employing three primary colors I, K and L additive to produce white, said receiver including in a cathode ray tube a multiplicity of phosphor strips laid down on a target in the cyclical order JKLK, and a switching grid adjacent said target with the conductors of said grid electron-optically aligned with said strips of color I, said receiver further including means to apply between the conductors of said switching grid a switching voltage at a frequency integrally related to the color subcarrier frequency, means to develop luminance and chrominance signals in separate channels, means to take a first sample of the chrominance signal at opposite phases of the color subcarrier cycle, one of said phases being the phase allocated to the color K, means to take a second sample of the chrominance at two opposite phases one-quarter cycle from said one phase, means to heterodyne said first sample with a voltage at a multiple of said subcarrierfrequency and toselect the heterodyne signal at the fourth harmonic of said switching frequency, means to heterodyne said second sample with a voltage at a multiple ofsaid subcarrier frequency and to select the heterodyne signal at the second harmonic of said switching frequency, means to apply the sum of said seccond and fourth harmonic signals to a first beam intensity controlling electrode in said tube, and means to apply to a second beam intensity controlling electrode in said tube a signal derived from said luminance signal.

10. A television receiver for the display of color television signals of the color subcarrier type employing three primary colors I, K and L additive to produce white, said receiver including in a cathode ray tube two electron beam intensity controlling electrodes, a switching grid of two sets of interlaced mutually insulated conductors and a multiplicity of phosphor strips laid down on a target in the cyclical order JKLK with adjacent strips of the color I aligned with adjacent of said conductors, said receiver further comprising means to develop luminance and chrominance signals in separate channels, means to take a first sample of the chrominance signal at opposite phases of the color 'subcarrier cycle, one of said phases being the phase allocated to the color K, means to take a second sample of the chrominance at two opposite phases onequarter cycle from said one phase, means to heterodyne said first sample with a voltage at a multiple of said subcarrier frequency and to select the heterodyne signal at the fourth harmonic of said subcarrier frequency, means to heterodyne said second sample with a voltage at a multiple of said subcarrier frequency and to select the hetero dyne signal at the second harmonic of said subcarrier frequency, means to apply the sum of said second and fourth harmonic signals to one of said electrodes, means to apply a signal derived from said luminance signal to the other of said electrodes, and means to apply between said sets of conductors a voltage at subcarrier frequency of such amplitude that the cathode ray beam in said tube is directed in the aggregate for substantially one-half the color subcarrier cycle to strips of the color K and for substantially one-quarter of the sub-carrier cycle to strips of each of the colors J and L.

References Cited in the file of this patent UNITED STATES PATENTS 2,866,127 Allwine Dec. 23, 1958 

1. A CATHODE RAY TUBE COMPRISING AN ELECTRON GUN, A TARGET AREA HAVING A MULTIPLICITY OF STRIPS OF MATERIAL DISPOSED THEREON IN SIDE-BY-SIDE RELATION, SAID STRIPS BEING LUMINESCENT ON ELECTRON IMPACT IN A PLURALITY OF PRIMARY COLORS J, K AND L ADDITIVE TO PRODUCE WHITE, AND A GRID INCLUDING TWO SETS OF INSULATED INTERLACED CONDUCTORS ARRANGED WITH SAID CONDUCTORS SUBSTANTIALLY PARALLEL TO SAID STRIPS BETWEEN SAID GUN AND TARGET AREA, ADJACENT OF SAID CONDUCTORS BEING ELECTRICALLY INSULATED FROM EACH OTHER AND ALTERNATE OF SAID CONDUCTORS BEING ELECTRICALLY CONNECTED TOGETHER, SAID STRIPS BEING LAID DOWN IN A REPEATING CYCLICAL ORDER JKLK WITH ADJACENT STRIPS OF THE COLOR J DISPOSED ELECTRON-OPTICALLY BEHIND ADJACENT OF SAID CONDUCTORS WITH RESPECT TO SAID GUN. 